Conventionally, a vehicle such as a car is equipped with safety devices such as seatbelts and airbags for protecting its driver and passengers from the shock at the time of a collision. Recently, to further improve the safety, pretensioner systems are becoming widely used in which an urgently-drawing device called pretensioner is disposed in a seatbelt winding system for winding up a seatbelt; and the seatbelt is instantaneously drawn by the pretensioner to restrain the body of an occupant so as not to collide with a steering wheel or the like. In such a pretensioner, because it is required to instantaneously wind up the seat belt, a gyro-type gas generator is used for a power source. More specifically, a piston is instantaneously moved in a cylinder by gas generated by combustion of gas generants in the gas generator. In conjunction with the piston, power is supplied to the pretensioner.
In many recent vehicles and so on, such pretensioner systems are used for all occupants. This increases the number of pretensioners installed in one vehicle or the like, and accordingly increases the number of gas generators installed. Therefore, gas generants to be used in such a gas generator have been desired that generate no CO gas or a smaller amount of CO gas. For example, the below Patent Documents 1 and 2 disclose gas generant compositions to solve the above problem.    Patent Document 1: Japanese Patent Unexamined Publication No. 2000-119088    Patent Document 2: Japanese Patent Unexamined Publication No. 2002-12492